Method for time synchronization of domain based on time information of vehicle

ABSTRACT

A time synchronization method performed by a communication node in a vehicle includes: receiving, from a road side unit (RSU), a first frame including time information of a first domain to which the RSU belongs; setting a time of the vehicle based on a time indicated by the time information of the first domain; and transmitting a second frame including the time information of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2016-0001326, filed on Jan. 6, 2016 in the KoreanIntellectual Property Office (KIPO), the entire contents of which areincorporated by reference as if fully set forth herein.

BACKGROUND

1. Technical Field

The present disclosure relates generally to methods for timesynchronization of domains, and more specifically, to methods for timesynchronization of independent domains based on time information ofvehicle.

2. Description of the Related Art

The number and variety of electronic devices installed within vehicleshave increased significantly along with the rapid digitalization ofvehicle parts. Electronic devices may currently be used throughout thevehicle, such as in a power train control system (including, e.g., anengine control system, an automatic transmission control system, or thelike), a body control system (including, e.g., a body electronicequipment control system, a convenience apparatus control system, a lampcontrol system, or the like), a chassis control system (including, e.g.,a steering apparatus control system, a brake control system, asuspension control system, or the like), a vehicle network (including,e.g., a controller area network (CAN), a FlexRay-based network, a mediaoriented system transport (MOST)-based network, or the like), amultimedia system (including, e.g., a navigation apparatus system, atelematics system, an infotainment system, or the like), and so forth.

Such systems and electronic devices constituting each of the abovesystems are connected via the vehicle network, which supports functionsof the electronic devices. For instance, the CAN may support atransmission rate of up to 1 Mbps and may support automaticretransmission of colliding messages, error detection based on a cycleredundancy interface (CRC), or the like. The FlexRay-based network maysupport a transmission rate of up to 10 Mbps and may supportsimultaneous transmission of data through two channels, synchronous datatransmission, or the like. The MOST-based network is a communicationnetwork for high-quality multimedia, which may support a transmissionrate of up to 150 Mbps.

Meanwhile, the telematics system, the infotainment system, as well asenhanced safety systems of the vehicle, require higher transmissionrates and system expandability. However, the CAN, FlexRay-based network,and the like may not sufficiently support such requirements. TheMOST-based network may support a higher transmission rate than the CANand the FlexRay-based networks. However, costs associated with applyingthe MOST-based network in all vehicle networks can be expensive. Due tothese limitations, an Ethernet-based network is often adopted as avehicle network. The Ethernet-based network may support bi-directionalcommunication through one pair of windings and may support atransmission rate of up to 10 Gbps.

Meanwhile, domains supporting a generalized precision time protocol(gPTP) in an industrial system may be classified into universal timedomains and working clock domains. The working clock domains may besynchronized with the universal time domain. However, in a case that aworking clock domain exists independently without any physicalconnection with the universal time domain, the working clock domaincannot be synchronized with the universal time domain.

SUMMARY

The present disclosure provides techniques for time synchronization ofan independent domain using time information of a vehicle.

In accordance with embodiments of the present disclosure, a timesynchronization method performed by a communication node in a vehicleincludes: receiving, from a road side unit (RSU), a first frameincluding time information of a first domain to which the RSU belongs;setting a time of the vehicle based on a time indicated by the timeinformation of the first domain; and transmitting a second frameincluding the time information of the vehicle.

Further, the first frame may include an identifier indicating a type ofthe first domain and position information of the first domain.

Further, the method may further include setting the time of the vehiclebased on the time information of the first domain when the first domainis a universal time domain.

Also, the method may further include measuring a link delay time betweenthe communication node and the RSU, and the time of the vehicle may beset to a sum of the time indicated by the time information of the firstdomain and the measured link delay time.

Further, the RSU may be a grand master node of the first domain.

Further, the method may further include: receiving the first framethrough a service channel between the vehicle and the first domain; andtransmitting the second frame through a service channel between thevehicle and a second domain.

Further, the second frame may include an identifier indicating a type ofthe first domain, update time information indicating a time at which thetime of the vehicle is updated, and position information of the firstdomain.

Further, the method may further include transmitting the second framewhen the vehicle is located within a second domain.

Also, the second domain may be a working clock domain.

Furthermore, in accordance with embodiments of the present disclosure, atime synchronization method performed by a road side unit (RSU) of aworking clock domain includes: receiving, from a communication node in avehicle, a synchronization frame including time information of thevehicle; and setting a time of the RSU based on a time indicated by thetime information of the vehicle. Time indicated by the time informationof the vehicle is synchronized with time of a universal time domain.

Also, the method may further comprise measuring a link delay timebetween the RSU and the communication node, and the time of the RSU maybe set to a sum of the time indicated by the time information of thevehicle and the measured link delay time.

Further, the method may further include receiving the synchronizationframe through a service channel between the working clock domain and thevehicle.

Further, the synchronization frame may include update time informationindicating a time at which the time of the vehicle is updated, anidentifier of the universal time domain, and position information of theuniversal time domain.

Also, the method may further include setting the time of the RSU basedon a time indicated by a synchronization frame having a latest updatetime among a plurality of synchronization frames when the plurality ofsynchronization frames are received.

Also, the method may further include setting the time of the RSU basedon a synchronization frame from a universal time domain closest to theRSU among a plurality of synchronization frames when the plurality ofsynchronization frames are received.

Further, the RSU may be a grand master node of the working clock domain.

According to embodiments of the present disclosure, a vehicle may obtaintime information of a universal time domain, and set its time based onthe obtained time information. Therefore, the time of the vehicle can besynchronized with the time of the universal time domain. After beingsynchronized with the universal time domain, the vehicle may notify thesynchronized time information. Then, working clock domains can obtainthe notified time information, and set their time based on the obtainedtime information. Thus, the working clock domains can be synchronizedwith the universal time domain.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure will become more apparent bydescribing in detail forms of the present disclosure with reference tothe accompanying drawings, in which:

FIG. 1 is a diagram showing a vehicle network topology according toembodiments of the present disclosure;

FIG. 2 is a diagram showing a communication node constituting a vehiclenetwork according to embodiments of the present disclosure;

FIG. 3 is a conceptual view showing an example of a time-aware network;

FIG. 4 is a conceptual view showing an example of arrangement ofdomains;

FIG. 5 is a conceptual view showing another example of arrangement ofdomains;

FIG. 6 is a conceptual view showing layers of WAVE;

FIG. 7 is a conceptual view showing IEEE 802.11p channels for V2Vcommunications;

FIG. 8 is a timing diagram showing frame transceiving procedure in IEEE802.11p;

FIG. 9 is a block diagram showing a WSMP frame;

FIG. 10 is a sequence chart showing a time synchronization methodaccording to embodiments of the present disclosure;

FIG. 11 is a conceptual view showing embodiments of a network to whichthe time synchronization method is applied;

FIG. 12 is an additional conceptual view showing embodiments of anetwork to which the time synchronization method is applied;

FIG. 13 is a flow chart showing a time synchronization procedure in anOBU;

FIG. 14 is a block diagram showing a synchronization frame according toembodiments of the present disclosure; and

FIG. 15 is a flow chart showing a time synchronization method performedin an independent domain.

It should be understood that the above-referenced drawings are notnecessarily to scale, presenting a somewhat simplified representation ofvarious preferred features illustrative of the basic principles of thedisclosure. The specific design features of the present disclosure,including, for example, specific dimensions, orientations, locations,and shapes, will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, forms of the present disclosure will be described in detailwith reference to the accompanying drawings. As those skilled in the artwould realize, the described forms may be modified in various differentways, all without departing from the spirit or scope of the presentdisclosure. Further, throughout the specification, like referencenumerals refer to like elements.

The terminology used herein is for the purpose of describing particularforms only and is not intended to be limiting of the disclosure. As usedherein, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, combustion, plug-in hybrid electric vehicles,hydrogen-powered vehicles and other alternative fuel vehicles (e.g.,fuels derived from resources other than petroleum).

Although forms are described herein as using a plurality of units toperform the exemplary process, it is understood that the exemplaryprocesses may also be performed by one or plurality of modules.Additionally, it is understood that the term controller/control unitrefers to a hardware device that includes a memory and a processor. Thememory is configured to store the modules, and the processor isspecifically configured to execute said modules to perform one or moreprocesses which are described further below. Moreover, it is understoodthat the units or modules described herein may embody acontroller/control unit for controlling operation of the unit or module.

Further, control logic of the present disclosure may be embodied asnon-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor,controller/control unit or the like. Examples of the computer readablemediums include, but are not limited to, ROM, RAM, compact disc(CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards andoptical data storage devices. The computer readable recording medium canalso be distributed in network coupled computer systems so that thecomputer readable media is stored and executed in a distributed fashion,e.g., by a telematics server or a Controller Area Network (CAN).

Since the present disclosure may be variously modified and have severalforms, specific embodiments will be shown in the accompanying drawingsand be described in detail in the detailed description. It should beunderstood, however, that it is not intended to limit the presentdisclosure to the specific embodiments but, on the contrary, the presentdisclosure is to cover all modifications and alternatives falling withinthe spirit and scope of the present disclosure.

Relational terms such as first, second, and the like may be used fordescribing various elements, but the elements should not be limited bythe terms. These terms are only used to distinguish one element fromanother. For example, a first component may be named a second componentwithout being departed from the scope of the present disclosure and thesecond component may also be similarly named the first component. Theterm ‘and/or’ means any one or a combination of a plurality of relatedand described items.

When it is mentioned that a certain component is “coupled with” or“connected with” another component, it should be understood that thecertain component is directly “coupled with” or “connected with” to theother component or a further component may be located therebetween. Incontrast, when it is mentioned that a certain component is “directlycoupled with” or “directly connected with” another component, it will beunderstood that a further component is not located therebetween.

Unless specifically stated or obvious from context, as used herein, theterm “about” is understood as within a range of normal tolerance in theart, for example within 2 standard deviations of the mean. “About” canbe understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%,0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear fromthe context, all numerical values provided herein are modified by theterm “about.”

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. Termssuch as terms that are generally used and have been in dictionariesshould be construed as having meanings matched with contextual meaningsin the art. In this description, unless defined clearly, terms are notideally, excessively construed as formal meanings.

Hereinafter, forms of the present disclosure will be described in detailwith reference to the accompanying drawings. In describing thedisclosure, to facilitate the entire understanding of the disclosure,like numbers refer to like elements throughout the description of thefigures and the repetitive description thereof will be omitted.

FIG. 1 is a diagram showing a vehicle network topology according toembodiments of the present disclosure.

As shown in FIG. 1, a communication node included in the vehicle networkmay be a gateway, a switch (or bridge), or an end node. The gateway 100may be connected with at least one switch 110, 110-1, 110-2, 120, and130 and may be configured to connect different networks. For example,the gateway 100 may support connection between a switch which supports acontroller area network (CAN) (e.g., FlexRay, media oriented systemtransport (MOST), local interconnect network (LIN), etc.) protocol and aswitch which supports an Ethernet protocol. Each of the switches 110,110-1, 110-2, 120, and 130 may be connected to at least one of end nodes111, 112, 113, 121, 122, 123, 131, 132, and 133. Each of the switches110, 110-1, 110-2, 120, and 130 may interconnect the end nodes 111, 112,113, 121, 122, 123, 131, 132, and 133, and control at least one of endnodes 111, 112, 113, 121, 122, 123, 131, 132, and 133 connected to theswitch.

The end nodes 111, 112, 113, 121, 122, 123, 131, 132, and 133 mayinclude an electronic control unit (ECU) configured to control varioustypes of devices mounted within a vehicle. For example, the end nodes111, 112, 113, 121, 122, 123, 131, 132, and 133 may include the ECUincluded in an infotainment device (e.g., a display device, a navigationdevice, an around view monitoring device, etc.).

The communication nodes (e.g., a gateway, a switch, an end node, or thelike) included in the vehicle network may be connected in a startopology, a bus topology, a ring topology, a tree topology, a meshtopology, or the like. In addition, the communication nodes of thevehicle network may support the CAN protocol, the FlexRay protocol, theMOST protocol, the LIN protocol, or the Ethernet protocol. Forms of thepresent disclosure may be applied to the foregoing network topologies.The network topology to which forms of the present disclosure may beapplied is not limited thereto and may be configured in various ways.

FIG. 2 is a diagram showing a communication node constituting a vehiclenetwork according to embodiments of the present disclosure. Notably, thevarious methods discussed herein below may be executed by a controllerhaving a processor and a memory.

As shown in FIG. 2, a communication node 200 of a network may include aPHY layer unit 210 and a controller unit 220. In addition, thecommunication node 200 may further include a regulator (not shown) forsupplying power. In particular, the controller unit 220 may beimplemented to include a medium access control (MAC) layer. A PHY layerunit 210 may be configured to receive or transmit signals from or toanother communication node. The controller unit 220 may be configured tocontrol the PHY layer unit 210 and perform various functions (e.g., aninfotainment function, or the like.). The PHY layer unit 210 and thecontroller unit 220 may be implemented as one system on chip (SoC), oralternatively may be implemented as separate chips.

Further, the PHY layer unit 210 and the controller unit 220 may beconnected via a media independent interface (MII) 230. The MII 230 mayinclude an interface defined in the IEEE 802.3 and may include a datainterface and a management interface between the PHY layer unit 210 andthe controller unit 220. One of a reduced MII (RMII), a gigabit MII(GMII), a reduced GMII (RGMII), a serial GMII (SGMII), a 10 GMII (XGMII)may be used instead of the MII 230. A data interface may include atransmission channel and a reception channel, each of which may have anindependent clock, data, and a control signal. The management interfacemay include a two-signal interface, one signal for the clock and onesignal for the data.

Particularly, the PHY layer unit 210 may include a PHY layer interfaceunit 211, a PHY layer processor 212, and a PHY layer memory 213. Theconfiguration of the PHY layer unit 210 is not limited thereto, and thePHY layer unit 210 may be configured in various ways. The PHY layerinterface unit 211 may be configured to transmit a signal received fromthe controller unit 220 to the PHY layer processor 212 and transmit asignal received from the PHY layer processor 212 to the controller unit220. The PHY layer processor 212 may be configured to execute operationsof the PHY layer interface unit 211 and the PHY layer memory 213. ThePHY layer processor 212 may be configured to modulate a signal to betransmitted or demodulate a received signal. The PHY layer processor 212may be configured to control the PHY layer memory 213 to input or outputa signal. The PHY layer memory 213 may be configured to store thereceived signal and output the stored signal based on a request from thePHY layer processor 212.

The controller unit 220 may be configured to monitor and control the PHYlayer unit 210 using the Mil 230. The controller unit 220 may include acontroller interface unit 221, a controller processor 222, a main memory223, and a sub memory 224. The configuration of the controller unit 220is not limited thereto, and the controller unit 220 may be configured invarious ways. The controller interface unit 221 may be configured toreceive a signal from the PHY layer unit 210 (e.g., the PHY layerinterface unit 211) or an upper layer (not shown), transmit the receivedsignal to the controller processor 222, and transmit the signal receivedfrom the controller processor 222 to the PHY layer unit 210 or upperlayer. The controller processor 222 may further include an independentmemory control logic or an integrated memory control logic forcontrolling the controller interface unit 221, the main memory 223, andthe sub memory 224. The memory control logic may be implemented to beincluded in the main memory 223 and the sub memory 224 or may beimplemented to be included in the controller processor 222.

Further, each of the main memory 223 and the sub memory 224 may beconfigured to store a signal processed by the controller processor 222and may be configured to output the stored signal based on a requestfrom the controller processor 222. The main memory 223 may be a volatilememory (e.g., a random access memory (RAM)) configured to temporarilystore data required for the operation of the controller processor 222.The sub memory 224 may be a non-volatile memory in which an operatingsystem code (e.g., a kernel and a device driver) and an applicationprogram code for performing a function of the controller unit 220 may bestored. A flash memory having a high processing speed, a hard disc drive(HDD), or a compact disc-read only memory (CD-ROM) for large capacitydata storage may be used as the non-volatile memory. Typically, thecontroller processor 222 may include a logic circuit having at least oneprocessing core. A core of an Advanced RISC Machines (ARM) family or acore of an Atom family may be used as the controller processor 222.

A method performed by a communication node and a correspondingcounterpart communication node in a vehicle network will be describedbelow. Although the method (e.g., signal transmission or reception)performed by a first communication node will be described below, themethod is applicable to a second communication node that corresponds tothe first communication node. In other words, when an operation of thefirst communication node is described, the second communication nodecorresponding thereto may be configured to perform an operation thatcorresponds to the operation of the first communication node.Additionally, when an operation of the second communication node isdescribed, the first communication node may be configured to perform anoperation that corresponds to an operation of a switch.

FIG. 3 is a conceptual view showing an example of a time-aware network.

As shown in FIG. 3, a time-aware network may support IEEE 802.1AS (e.g.,a generalized precision time protocol (g IP), or the like), and maycomprise a universal time domain 3100, and a working clock domain 3200.Here, gPTP operations and time scales of respective domains may beindependent from each other. Each of the domains belonging to thetime-aware network may have its unique number (i.e., unique identifier).For example, the unique number may a value in a range of 0 to 127.However, the range of the unique number is not limited to the aboveexample. That is, the range may exceed 127. In an industrial system, theunique number of the universal time domain 3100 may be set to ‘0,’ andthe unique number of the working clock domain may be set to one of 1 to127. The domain, in the industrial system, may represent a country, acity, or a specific area belonging to a city.

Each of the universal time domain 3100 and the working clock domain 3200may comprise a plurality of communication nodes. Also, communicationsnodes 3112, 3116, 3121, and 3122 belonging to both of the domains 3100and 3200 may exist. A communication node may be a grand master node, aswitch (or, bridge), or an end node. The communication nodes may beconnected physically.

In the universal time domain 3100, a first grand master node 3110 may bea communication node in an uppermost level. The first grand master node3110 may support a global positioning system (GPS). For example, thefirst grand master node 3110 may use the GPS to identify its positionand notify its identified position. The communication nodes belonging tothe universal time domain 3100 may operate based on time of the firstgrand master node 3110. For example, the communication nodes belongingto the universal time domain 3100 may be synchronized with the firstgrand master node 3110.

The first grand master node 3110 may be connected with a first switch3111 and a second switch 3112. Also, the first switch 3111 may beconnected to a third switch 3113, a fourth switch 3114, and a fifthswitch 3115. The second switch 3112 may be connected to a second grandmaster node 3210, a sixth switch 3116, a seventh switch 3117, an eighthend node 3213. The third switch 3113 may be connected to a first endnode 3117 and a second end node 3118. The fourth switch 3114 may beconnected to a third end node 3119, and the fifth switch 3115 may beconnected to a fourth end node 3120. The sixth switch 3116 may beconnected to a fifth end node 3121 and a sixth end node 3122.

In the working clock domain 3200, the second grand master node 3210 maybe a communication node in an uppermost level. The second grand masternode 3210 may be synchronized with the first grand master node 3110.That is, the time of the working clock domain 3200 may be synchronizedwith the time of the universal time domain 3100. Alternatively, the timeof the working clock domain 3200 may be configured based on anoscillator of the corresponding area. The communication nodes belongingto the working clock domain 3200 may operate based on the time of thesecond grand master node 3210. The second grand master node 3210 may beconnected to the second switch 3112. The second switch 3112 may beconnected to the first grand master node 3110, the sixth switch 3116,the seventh switch 3211, and the eighth end node 3213. The seventhswitch 3211 may be connected to the seventh end node 3212.

The time-aware network may have various configurations without beingrestricted to the above example. In the time-aware network, domains maybe arranged as follows.

FIG. 4 is a conceptual view showing an example of arrangement ofdomains. As shown in FIG. 4, a programmable logic controller (PLC) basedfactory network may comprise a plurality of domains 4100, 4200, and4300. A universal time domain 4100 may comprise a first working clockdomain 4200 and a second working clock domain 4300. The communicationnodes included in the universal time domain 4100 may operate based ontime of a first grand master node 4110. The first working clock domain4200 may be connected physically to the universal time domain 4100. Forexample, a second grand master node 4210 may be physically connected toa switch included in the universal time domain 4100. In this case, thesecond grand master node 4210 may be synchronized with the first grandmaster node 4110, and the communication nodes in the first working clockdomain 4200 may operate based on time of the second grand master node4210. Alternatively, the communication nodes include in the firstworking clock domain 4200 may operate based on time independent fromthat of the universal time domain 4100. The first working clock domain4200 may be physically connected to the second working clock domain4300.

The second working clock domain 4300 may be physically connected to theuniversal time domain 4100. For example, switches included in the secondworking clock domain 4300 may be physically connected to switchesincluded in the universal time domain 4100. In this case, a second grandmaster node 4310 may be synchronized with the first grand master node4110, and the communication nodes included in the second working clockdomain 4300 may operate based on time of the third grand master node4310. Alternatively, the communication nodes included in the secondworking clock domain 4300 may operate based on time independent fromthat of the universal time domain 4100.

FIG. 5 is a conceptual view showing another example of arrangement ofdomains.

As shown in FIG. 5, a PLC based factory network may comprise a pluralityof domains 5100, 5200, and 5300. The plurality of working clock domains5100, 5200, and 5300 may be connected to each other. For example, asecond grand master node 5210 of the second working clock domain 5200may be connected with a switch included in the first working clockdomain 5100, and a third grand master node 5310 of the third workingclock domain 5300 may be connected to a switch included in the firstworking clock domain 5100. In this case, the first working clock domain5100 may operate as a primary domain, and the second working clockdomain 5200 and the third working clock domain 5300 may operate as subdomains.

Thus, the second grand master node 5210 may be synchronized with thefirst grand master node 5110, and communication nodes included in thesecond working clock domain 5200 may operate based on time of the secondgrand master node 5210. A third grand master node 5310 may besynchronized with the first grand master node 5110, and communicationnodes included in the third working clock domain 5300 may operate basedon time of the third grand master node 5310.

Alternatively, the working clock domains 5100, 5200, and 5300 may beseparated from each other. In this case, the working clock domains 5100,5200, and 5300 may operate based on independent times, and accordinglysynchronization among them may not be established. Meanwhile, in thecase that synchronization among domains in the time-aware factorynetwork is not acquired, the nodes belonging to the factory network maymalfunction.

On the other hand, a wireless access in vehicular environment (WAVE) isan intelligent transportation system (ITS) communication technology forproviding high-speed vehicles with communication services, and modifiedto be suitable for vehicular environments from a wireless local areanetwork (WLAN) technology. The WAVE may support avehicle-to-infrastructure (V2I) or vehicle-to-vehicle (V2V)communication which is a type of dedicated short range communication(DSRC) technologies.

IEEE 802.11a/g, which is one of the conventional WLAN technologies, maybe suitable to indoor environments, and does not support mobility. Onthe contrary, the WAVE can support mobility, and support reliablecommunications even in outdoor environments where interferences due toDoppler shifts exist. For example, the WAVE can support a fast linkconnection between an on-board unit (OBU) installed in a vehicle movingat a velocity up to maximum of 160 Km/h and a road-side unit (RSU)installed in road side, and high-speed data communications up to 27Mbps. The WAVE has the following layers.

FIG. 6 is a conceptual view showing layers of WAVE.

As shown in FIG. 6, the WAVE model may comprise a physical (PHY) layer610, a medium access control (MAC) layer 620, a logical link control(LLC) layer 630, a networking service layer 640, and an upper layer 650.The PHY layer 610 may support IEEE 802.11p, etc., and correspond to aPHY layer according to an open system interconnection (OSI) referencemodel. The MAC layer 620 may support IEEE 1609.4, IEEE 802.11, etc., andcorrespond to a data link layer according to the OSI reference model.The LLC layer 630 may support IEEE 802.2, etc., and correspond to a datalink layer according to the OSI reference model.

The networking service layer 640 may support IEEE 1609.1, IEEE 1609.3,or the like, and correspond to a network layer and a transport layeraccording to the OSI reference model. The upper layer 650 may supportapplication programs, a DSRC message set, or the like, and correspond toa session layer, a presentation layer, and an application layeraccording to the OSI reference model. The MAC layer 620, networkingservice layer 640, and upper layer 650 may support security servicesdefined in IEEE 1609.2.

Meanwhile, the IEEE 802.11p is a standard for V2V communications, andmay interoperate with the IEEE 1609 series standards defining a channelaccess procedure of a vehicle in a multi-channel environment. Thechannels for V2V communications are defined in the IEEE 802.11p asfollows.

FIG. 7 is a conceptual view showing IEEE 802.11p channels for V2Vcommunications.

As shown in FIG. 7, a synchronization period may have the length of 100ms. 50 ms of the synchronization period may be configured to be acontrol channel (CCH) duration, and the rest 50 ms of thesynchronization period may be configured to be a service channel (SCH)duration. A single CCH may be configured in the CCH duration, and aframe comprising control information, management information,safety-related information, high priority information, etc. may betransmitted through the CCH. For example, multi-channel synchronizationinformation, channel access information, vendor-specific information,master information block (MIB) maintenance information, readdressinginformation, other IEEE 802.11 service information, or the like may betransmitted through the CCH. Six SCHs may be configured in the SCHduration, and user information, data, or the like may be transmittedthrough the SCHs.

Meanwhile, frames can be transmitted and received in the IEEE 802.11p asfollows.

FIG. 8 is a timing diagram showing frame transceiving procedure in IEEE802.11p.

As shown in FIG. 8, in a case that a CCH is in idle state in the CCHduration, a RSU may perform a random backoff procedure. For example, ina case that the CCH is maintained in the idle state during a contentionwindow (CW) duration according to the random backoff procedure, the RSUmay transmit a WAVE service advertisement (WSA) frame 801 through theCCH. Also, the RSU may transmit a safety application (APP) related frame802 through the CCH after a lapse of a distributed interface space(DIFS) from an end point of the WSA frame 801. Also, the RSU maytransmit a safety APP related frame 803 through the CCH after a lapse ofan arbitration interframe space (AIFS) from an end point of the safetyAPP related frame 802.

Meanwhile, in a case that a SCH is in idle state in the SCH duration, anOBU may perform a random backoff procedure. For example, in a case thatthe SCH is maintained in the idle state during a CW duration accordingto the random backoff procedure, the OBU may transmit a request-to-send(RTS) frame 804 through the SCH. The OBU may receive a clear-to-send(CTS) frame 805 from one of other communication nodes (e.g., an RSU oranother OBU, etc.) after a lapse of a SIFS from an end point of the RTSframe 804. Also, the OBU may transmit a data frame 806 through the SCHafter a lapse of a SIFS from an end point of the CTS frame 805. The OBUmay receive an acknowledgement (ACK) frame 807 through the SCH after alapse of a SIFS from an end point of the data frame 806. In a case thatthe OBU successfully receives the ACK frame 807 in response to the dataframe 806, the OBU may determine that the data frame 806 has beensuccessfully received at the corresponding communication node.

Meanwhile, the communication nodes (e.g., the OBU, the RSU, etc.) mayperform communications based on a WAVE short message protocol (WSMP).For example, V2I communications between RSU and OBU may be performedbased on the WSMP, and V2V communications between OBUs may also beperformed based on the WSMP. The WSPM used for the communicationsbetween communication nodes will be described.

FIG. 9 is a block diagram showing a WSMP frame.

As shown in FIG. 9, a WSMP frame 900 may comprise a WSMP header and aWSM data field 960. A user data having the length of at most 512 bytesmay be transmitted through the WSMP frame 900. Also, the WSMP header maycomprise a version field 910, a provider service identifier (PSID) field920, an extension field 930, a WSMP WAVE element identifier (ID) field940, and a length field 950. The version field may have the length of 1byte, and indicate a version of WSMP. The PSID field may have the lengthof 4 bytes, and include an identifier of a service provided by a serviceprovider.

The extension field 930 may comprise information on a channel number, atransmission rate, a transmission power, or the like, and the length ofthe extension field 930 may be variable. The WSMP WAVE element ID field940 may have the length of 1 byte, and include an identifier of WAVEelements. The length field 950 may have the length of 2 bytes, andindicate the length of the WSM data field 960. The WSM data field 960may comprise data used by an upper layer, and the length of the WSM datafield may be variable.

On the other hand, for time synchronization of the above-describeddomains, the domains should be physically connected with each other.Therefore, a domain existing independently without a physical connection(hereinafter, referred to as an “independent domain”) may not besynchronized with other domains. However, when a communication node withmobility (e.g., a communication node included in a vehicle) exists, thecommunication node may notify its domain time information, andcommunication nodes belonging to the domain may be synchronized based onthe notified time information. In the below description, a timesynchronization method by a communication node with mobility will beexplained.

FIG. 10 is a sequence chart showing a time synchronization methodaccording to embodiments of the present disclosure, FIG. 11 is aconceptual view showing embodiments of a network to which the timesynchronization method is applied, and FIG. 12 is an additionalconceptual view showing embodiments of a network to which the timesynchronization method is applied.

As shown in FIGS. 10 to 12, a network may comprise a universal timedomain 1110, a first working clock domain 1120, and a second workingclock domain 1130. The domains 1110, 1120, and 1130 may existindependently from each other without physical connections. A first RSU1111 may be a grand master node of the universal time domain 1110, asecond RSU 1121 may be a grand master node of the first working clockdomain 1120, and a third RSU 1131 may be a grand master node of thesecond working clock domain 1130. The OBU 1150 may be a communicationnode having mobility. For example, the OBU 1150 may be a communicationnode included in a vehicle, and the vehicle may form a domain.

The first RSU 1111 may generate a notification frame including timeinformation indicating its time (e.g., reference time). Also, thenotification frame may further comprise information on a position of thefirst RSU 1111 (e.g., latitude and longitude). For example, when thefirst RSU 1111 supports GPS, the first RSU 1111 may identify itsposition through the GPS, and generate the notification frame by usingthe identified position. Also, the notification frame may furthercomprise priority information (e.g., type identifier) indicating thetype of the domain to which the first RSU 1111 belongs. For example,since the first RSU 1111 belongs to the universal time domain 1110, thepriority information of the notification frame of the first RSU 1111 maybe set to ‘0.’

The notification frame may be generated based on the WSMP, and the timeinformation, position information, and priority information may beincluded in a WSM data field of the notification frame. Here, the timeinformation of the first RSU 1111 indicates time information of theuniversal time domain 1110, the position information of the first RSU1111 indicates position information of the universal time domain 1110.The first RSU 1111 may transmit the notification frame periodically ornon-periodically (S1000). The notification frame may be transmittedthrough a CCH or a SCH between the first RSU 1111 and the OBU 1150.

When the OBU 1150 is located within communication coverage of the firstRSU 1111, the OBU 1150 can receive the notification frame from the firstRSU 1111, and perform a time synchronization procedure with the firstRSU 1111 based on the received notification frame (S1010). The timesynchronization procedure between the OBU 1150 and the first RSU 1111may be performed as follows.

FIG. 13 is a flow chart showing a time synchronization procedure in anOBU.

As shown in FIG. 13, the OBU 1150 may obtain the priority informationfrom the notification frame, and identify the type of the domain towhich the first RSU 1111 belongs based on the obtained priorityinformation (S1300). For example, in the case that the priorityinformation is set to ‘0,’ the OBU 1150 may determine that the first RSU1111 belongs to the universal time domain. In the case that the firstRSU 1111 belongs to the universal time domain, the OBU 1150 may obtainthe time information and the position information of the universal timedomain from the notification frame. On the contrary, in the case thatthe priority information is set to one of ‘1’ to ‘7,’ the OBU 1150 maydetermine that the first RSU 1111 belongs to a working clock domain. Inthe case that the first RSU 1111 belongs to the working clock domain,the OBU 1150 may discard the received notification frame.

In the case that the first RSU 1111 belongs to the universal timedomain, the OBU 1150 may measure a link delay time with the first RSU1111 (S1310). For example, the OBU 1150 may transmit a delay requestframe to the first RSU 1111, and record a transmission time of the delayrequest frame (hereinafter, ‘RSU1_(time1)’). The first RSU 1111 mayreceive the delay request frame the OBU 1150, and record a receptiontime of the delay request frame (hereinafter, ‘RSU1_(time2)’). The firstRSU 1111 may transmit a delay response frame including informationindicating the RSU1_(time2) to the OBU 1150, record a transmission timeof the delay response frame (hereinafter, ‘RSU1_(time3)’), and transmita follow-up frame including information indicating the RSU1_(time3) tothe OBU 1150. The follow-up message may be transmitted immediately afterthe transmission of the delay response frame.

The OBU 1150 may receive the delay response frame from the first RSU1111, record the reception time of the delay response frame(hereinafter, ‘RSU1_(time4)’), and obtain the RSU1_(time2) from thedelay response frame. Also, the OBU 1150 may receive the follow-up framefrom the first RSU 1111, and obtain the RSU1_(time3) from the follow-upframe. The frames used for the link delay time measurement may betransmitted through a CCH or SCH between the OBU 1150 and the first RSU1111. The OBU 1150 may measure the link delay time between the OBU 1150and the first RSU 1111 based on the following Equation 1.

$\begin{matrix}{{{link}\mspace{14mu} {delay}\mspace{14mu} {time}} = \frac{\begin{matrix}{\left( {{{RSU}\; 1_{{time}\; 2}} - {{RSU}\; 1_{{time}\; 1}}} \right) +} \\\left( {{{RSU}\; 1_{{time}\; 4}} - {{RSU}\; 1_{{time}\; 3}}} \right)\end{matrix}}{2}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Alternatively, in the case that the OBU 1150 supports GPS, the OBU 1150may identify its position using the GPS, and identify the positioninformation of the first RSU 1111 from the notification frame. In thiscase, the OBU 1150 may calculate a distance between the OBU 1150 and thefirst RSU 1111 based on the positions of the OBU 1150 and the first RSU1111, and estimate the link delay time between the OBU 1150 and thefirst RSU 1111.

The OBU 1150 may set its time based on a value of ‘time indicated by thetime information of the notification frame+link delay time’ (S1320).Therefore, the time of the OBU 1150 may be synchronized with the time ofthe universal time domain 1110. Here, the procedure of measuring thelink delay time may be skipped. In this case, the OBU 1150 may set itstime simply with the time indicated by the time information of thenotification frame.

Referring again to FIGS. 10 to 12, the vehicle including the OBU 1150may move. When the vehicle moves into another domain, the OBU 1150 maytransmit a connection request frame to the corresponding domain (e.g.,the second RSU 1121 belonging to the first working clock domain 1120)(S1020). Also, the OBU 1150 may record a transmission time of theconnection request frame (hereinafter, ‘RSU2_(time1)’). For example, theOBU 1150 supporting GPS may identify its position change according tothe movement of the vehicle by using the GPS, and determine that thevehicle has moved into another domain based on the identified position.Alternatively, the OBU 1150 may measure a strength of a signal receivedfrom the first RSU 1111, and may determine that the vehicle has movedinto other domain when the measured strength of the signal is equal toor less than a predetermined threshold. The connection request frame mayinclude an identifier of the OBU 1150, and may be generated based on theWSMP. The connection request frame may be transmitted through a CCH orSCH between the OBU 1150 and the second RSU 1121.

The second RSU 1121 may receive the connection request frame the OBU1150, and record a reception time of the connection request frame(hereinafter, ‘RSU2_(time2)’). The second RSU 1121 may generate aconnection response frame including information indicating theRSU2_(time2). Also, the connection response frame may further includepriority information and position information of the working clockdomain 1120 to which the second RSU 1121 belongs, and SCH-relatedinformation (e.g., information on a frequency resource and time resourcein which the SCH is configured). The priority of the first working clockdomain 1120 may be set to one of ‘1’ to ‘7.’ The connection responseframe may be generated based on the WSMP, and a WSM data field maycomprise the information indicating the RSU2_(time2), the priorityinformation, the position information, and the SCH-related information.

The second RSU 1121 may transmit the connection response frame to theOBU 1150 (S1030). Also, the second RSU 1121 may record a transmissiontime of the connection response frame (hereinafter, ‘RSU2_(time3)’),generate a follow-up frame including information indicating theRSU2_(time3), and transmit the generated follow-up frame to the OBU 1150(S1040). The follow-up frame may be transmitted immediately after thetransmission of the connection response frame. The connection responseframe and the follow-up frame may be transmitted through a CCH or SCHbetween the OBU 1150 and the second RSU 1121.

The OBU 1150 may receive the connection response frame from the secondRSU 1121, record a reception time of the connection response frame(hereinafter, ‘RSU2_(time4)’), and obtain the RSU2_(time2) from theconnection response frame. Also, the OBU 1150 may receive the follow-upframe from the second RSU 1121, and obtain the RSU2_(time3) included inthe follow-up frame. The OBU 1150 may measure the link delay timebetween the OBU 1150 and the second RSU 1121 based on the followingEquation 2.

$\begin{matrix}{{{link}\mspace{14mu} {delay}\mspace{14mu} {time}} = \frac{\begin{matrix}{\left( {{{RSU}\; 2_{{time}\; 2}} - {{RSU}\; 2_{{time}\; 1}}} \right) +} \\\left( {{{RSU}\; 2_{{time}\; 4}} - {{RSU}\; 2_{{time}\; 3}}} \right)\end{matrix}}{2}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Alternatively, in the case that the OBU 1150 supports GPS, the OBU 1150may identify its position using the GPS, and identify the positioninformation of the second RSU 1121 from the connection response frame.In this case, the OBU 1150 may calculate a distance between the OBU 1150and the second RSU 1121 based on the positions of the OBU 1150 and thesecond RSU 1121, and estimate the link delay time between the OBU 1150and the second RSU 1121.

The OBU 1150 may generate a synchronization frame (S1050). For example,in the case that a working clock domain to which the second RSU 1121belongs is an independent domain, the OBU 1150 may generate thesynchronization frame. The synchronization frame may be generated basedon the WSMP, and constructed as follows.

FIG. 14 is a block diagram showing a synchronization frame according toembodiments of the present disclosure.

As shown in FIG. 14, a synchronization frame 1400 may comprise a WSMPheader and a WSM data field 1460. A user data having the length of atmost 512 bytes may be transmitted through the synchronization frame1400. Also, the WSMP header may comprise a version field 1410, a PSIDfield 1420, an extension field 1430, a WSMP WAVE element ID field 1440,and a length field 1450. The fields included in the WSMP header of thesynchronization frame 1400 may be identical to or similar with those ofthe WSMP header of the WSMP frame 900 explained referring to FIG. 9.

The WSM data field 1460 may comprise a priority information field 1461,an update time field 1462, a position information field 1463, and a timeinformation field 1464. The length of the WSM data field 1460 may bevariable. The priority information field 1461 may have the length of 3bits, and indicate the type of a domain to which the RSUtime-synchronized with the OBU belongs. For example, the priorityinformation field 1461 may have a value of ‘0’ to ‘7.’ The priorityfield 1461 configured as ‘0’ may indicate that the domain of the RSU isthe universal time domain, and the priority field 1461 configured as oneof ‘1’ to ‘7’ may indicate that the domain of the RSU is a working clockdomain.

The update time field 1462 may have the length of 8 bits, and indicate atime at which the time of the OBU was updated. The position informationfield 1463 may have the length of 6 bits, and indicate the positioninformation (i.e., position information of the domain to which the RSUbelongs) of the RSU time-synchronized with the OBU. The positioninformation may comprise information of latitude and longitude. The timeinformation field 1464 may indicate the time of the OBU. The length ofthe time information field 1464 may be variable.

Referring again to FIGS. 10 to 12, the priority information field 1461of the synchronization frame may indicate the type of the universal timedomain to which the first RSU 1111 belongs, the update time field 1462may indicate the time at which the time of OBU 1150 became synchronizedwith the time of the first RSU 1111, the position information field 1463may indicate the position of the first RSU 1111, and the timeinformation field 1464 may indicate the time of the OBU 1150. Also, thesynchronization frame may further comprise information indicating thelink delay time between the OBU 1150 and the second RSU 1121. The OBU1150 may transmit the synchronization frame to the second RSU 1121(S1060). The synchronization frame may be transmitted through a CCH orSCH between the OBU 1150 and the second RSU 1121. For example, thesynchronization frame may be transmitted through a SCH indicated by theSCH-related information included in the connection response frame.

The second RSU 1121 may receive the synchronization frame from the OBU1150, and perform time synchronization based on the information includedin the synchronization frame (S1070). For example, the second RSU 1121may identify the type of the domain from the priority information field1261 of the synchronization frame. In the case that the type of thedomain indicates the universal time domain, the second RSU 1121 mayconfigure the time of the second RSU 1121 based on the time indicated bythe time information field 1464 of the synchronization frame. Here, thesecond RSU 1121 may configure the time of the second RSU 1121 based on‘time indicated by the time information field 1464+link delay time.’Accordingly, the time of the working clock domain 1120 may besynchronized with the time of the universal time domain 1110.

Meanwhile, the second RSU 1121 having received multiple synchronizationframes may perform time synchronization as follows.

FIG. 15 is a flow chart showing a time synchronization method performedin an independent domain.

As shown in FIG. 15, the second RSU 1121 may receive a plurality ofsynchronization frames from a plurality of OBUs (S1500). The second RSU1121 may identify types of the respective domains from the priorityinformation fields included in the plurality of synchronization frames(S1510). For example, in the case that the priority information field ofthe received synchronization frame is set to ‘0,’ the second RSU 1121may identify the type of the domain to which the corresponding OBUbelongs as the universal time domain. On the contrary, in the case thatthe priority information field of the received synchronization frame isset to a value of ‘1’ to ‘7,’ the second RSU 1121 may identify the typeof the domain to which the corresponding OBU belongs as the workingclock domain. In the case that the type of the domain is the workingclock domain, the second RSU 1121 may discard the correspondingsynchronization frame (S1520).

When a single synchronization frame including information indicating theuniversal time domain type exists, the second RSU 1121 may perform timesynchronization of the second RSU 1121 based on the time informationincluded in the corresponding synchronization frame (S1550). However,when a plurality of synchronization frames indicating the universal timedomain type exist, the second RSU 1121 may identify update timesindicated by the respective update time fields of the plurality ofsynchronization frames, and identify a synchronization frame having thelatest update time (S1530). The second RSU 1121 may discardsynchronization frames except the synchronization frame having thelatest update time (S1520).

When a single synchronization frame having the latest update timeexists, the second RSU 1121 may perform time synchronization of it basedon the time information included in the corresponding synchronizationframe (S1550). When a plurality of synchronization frames having thelatest update time exist (i.e., a plurality of synchronization frameshaving the same update time exist), the RSU may identify positions ofthe respective OBUs based on position information fields of theplurality of synchronization frames. The second RSU 1121 may identifydistances from the second RSU 1121 to the respective universal timedomains based on the position information, and identify thesynchronization frame of the closest universal time domain (S1540). Thesecond RSU 1121 may discard synchronization frames except thesynchronization frame of the closest universal time domain (S1520). Thesecond RSU 1121 may perform time synchronization based on the timeinformation included in the synchronization frame including informationon the closest universal time domain (S1550).

In FIG. 11, the second RSU 1121 may be physically connected with thesecond working clock domain 1130. Accordingly the third RSU 1131 mayobtain time information from the second RSU 1121, and set its time basedon the time indicated by the obtained time information. Thus, the secondworking clock domain 1130 may be synchronized with the universal timedomain 1110. In FIG. 12, the third RSU 1131 of the second working clockdomain 1130 may receive the synchronization frame from the OBU 1150 in amanner identical or similar to the above-described method, and set itstime according to the information included in the synchronization frame.Accordingly, the second working clock domain 1130 may be synchronizedwith the universal time domain 1110.

The methods according to embodiments of the present disclosure may beimplemented as program instructions executable by a variety of computersand recorded on a computer readable medium. The computer readable mediummay include a program instruction, a data file, a data structure, or acombination thereof. The program instructions recorded on the computerreadable medium may be designed and configured specifically for thepresent disclosure or can be publicly known and available to those whoare skilled in the field of computer software. Examples of the computerreadable medium may include a hardware device such as ROM, RAM, andflash memory, which are specifically configured to store and execute theprogram instructions. Examples of the program instructions includemachine codes made by, for example, a compiler, as well as high-levellanguage codes executable by a computer, using an interpreter. The aboveexemplary hardware device can be configured to operate as at least onesoftware module in order to perform the operation of the presentdisclosure, and vice versa.

While the embodiments of the present disclosure and their advantageshave been described in detail above, it should be understood thatvarious changes, substitutions and alterations may be made hereinwithout departing from the scope of the disclosure.

What is claimed is:
 1. A time synchronization method performed by acommunication node in a vehicle, the method comprising: receiving, froma road side unit (RSU), a first frame including time information of afirst domain to which the RSU belongs; setting a time of the vehiclebased on a time indicated by the time information of the first domain;and transmitting a second frame including the time information of thevehicle.
 2. The time synchronization method according to claim 1,wherein the first frame includes an identifier indicating a type of thefirst domain and position information of the first domain.
 3. The timesynchronization method according to claim 1, further comprising settingthe time of the vehicle based on the time information of the firstdomain when the first domain is a universal time domain.
 4. The timesynchronization method according to claim 1, further comprisingmeasuring a link delay time between the communication node and the RSU,wherein the time of the vehicle is set to a sum of the time indicated bythe time information of the first domain and the measured link delaytime.
 5. The time synchronization method according to claim 1, whereinthe RSU is a grand master node of the first domain.
 6. The timesynchronization method according to claim 1, further comprising:receiving the first frame through a service channel between the vehicleand the first domain; and transmitting the second frame through aservice channel between the vehicle and a second domain.
 7. The timesynchronization method according to claim 1, wherein the second frameincludes an identifier indicating a type of the first domain, updatetime information indicating a time at which the time of the vehicle isupdated, and position information of the first domain.
 8. The timesynchronization method according to claim 1, further comprisingtransmitting the second frame when the vehicle is located within asecond domain.
 9. The time synchronization method according to claim 8,wherein the second domain is a working clock domain.
 10. A timesynchronization method performed by a road side unit (RSU) of a workingclock domain, the method comprising: receiving, from a communicationnode in a vehicle, a synchronization frame including time information ofthe vehicle; and setting a time of the RSU based on a time indicated bythe time information of the vehicle, wherein the time indicated by thetime information of the vehicle is synchronized with a time of auniversal time domain.
 11. The time synchronization method according toclaim 10, further comprising measuring a link delay time between the RSUand the communication node, wherein the time of the RSU is set to a sumof the time indicated by the time information of the vehicle and themeasured link delay time.
 12. The time synchronization method accordingto claim 10, further comprising receiving the synchronization framethrough a service channel between the working clock domain and thevehicle.
 13. The time synchronization method according to claim 10,wherein the synchronization frame includes update time informationindicating a time at which the time of the vehicle is updated, anidentifier of the universal time domain, and position information of theuniversal time domain.
 14. The time synchronization method according toclaim 13, further comprising setting the time of the RSU based on a timeindicated by a synchronization frame having a latest update time among aplurality of synchronization frames when the plurality ofsynchronization frames are received.
 15. The time synchronization methodaccording to claim 13, further comprising setting the time of the RSUbased on a synchronization frame from a universal time domain closest tothe RSU among a plurality of synchronization frames when the pluralityof synchronization frames are received.
 16. The time synchronizationmethod according to claim 10, wherein the RSU is a grand master node ofthe working clock domain.